Relay control system



March 7, 1944. I M, E, REAGAN ,3 3, 2

RELAY CONTROL SYSTEMS Filed July 19, 1940 .UZ 1 I U2 14 15 g J E z 1 2 194" 2 1 2 Current WITNESSES: v Z INVENTOR Patented Mar. 7, 1944- RELAY CONTROL SYSTEM Maurice E. Reagan, Pittsburgh, Pa.,. assignor to Westinghouse-Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of.

Pennsylvania Application July 19', 1940, Serial'No. 346,267

2 Claims.

My invention relates, generally, to control systems and, more particularly, to voltage-responsive relay control systems utilizing a relay to effect control functions in accordance with the degree in voltage variation of a circuit or the degree of unbalance between the voltages of two circuits or different parts of" the same circuit.

Heretofore, relays of the differential or balance type have been used to perform variouscontrol functions in accordance with relative values of voltage between two circuits by simply con meeting the opposed or differentially related operating windings of the relay across the circuits in series with a common resistor. While this type of connection has been satisfactory to a certain extent, it has been found that it is not altogether satisfactory for the-reason that it is not sensitive to small variations in thevoltages of the circuits and there are many applicationswhichrequirea high degree of sensitivity of control. This defect is not only present in differential relay control systems but also in systems employing a single voltage responsive relay where itis highly desirable that the relay function quickly and positively on a small voltage variation in its supply circuit.

Accordingly, it is theobject of my invention; generally stated, to provide a relay control system which'is simple and economical to manufacture andwhich has a high degree of sensitivity.

A more specific object of'my invention is" to provide for magnifying the-degree of energization of theoperating winding of a control relay to increase the sensitivity thereof in responseto small voltagechanges.

A further object of my invention is to providefor increasing the sensitivity of a voltage responsive relay device'by utilizing a conductive member which has the inherent characteristic of varying its resistance greatly with current density to magnify the operating'current of the relay in response to a predetermined change in the voltage of its supply circuit.

A still further object of my invention is to provide for utilizing a current'rectiiier device of the dry contact type to increase the'sensitivity of a relay connected to effect control functions'in response to the variationsin the voltage of an electric circuit to which it is connected.

Another object of my invention is to provide for increasing the sensitivity and-'magni'tudeof' unbalance in a differential or balance relaycontrol system by connecting a current rectifier device of the dry contact type in series with each of the opposed operating winding of the relay.

These and other objects of my invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawing wherein:

Figure l is a diagrammatic view of a circuit simulating a balance relay control system illustrat'ing the principles of my invention;

Fig, 2 is a diagrammatic view of a balance relay control system embodying the principal features of my invention;

Fig. 3 is a view illustrating relative degrees of current unbalance in the opposed operating windingsof a balancerelay with and without the use of current rectifier devices connected inthe circuits of the windings.-

In practicing my invention in its basic form a current rectifier device or element of the dry contact type such, for example, asa copper-oxide rectifier, is connected in series circuit relation with the operating winding or windings of the relay so as to automatically increase or magnify the current flow therein resulting from a predetermine'd' change in the voltage of the circuit or circuits towhich the relay is connected.

Referring now to the drawing, there is illustrated'a differential or balance relay control system embodying the principles of theinvention. It is to be understood, however, that the'principlesinvolved may be applied to'other forms of relay control systems wherever it is desired to increase the sensitivity of the relay to predetermined voltage changes.

The principles of the invention are illustrated best inFig. 1 wherein one circuit or a portion of a circuit is represented by conductors l0 and II and another circuit or a part of the same circuit is illustrated by conductors I2 and I3, having voltages E1 and E2, respectively, thereon.

If ammeters l4 and iii are connected across these circuits in series with a common resistor it, which may be adjustable if desired; the currentsli and I2, flowing in the ammeter circuits will be proportional to the voltages E1 and-E2 and these currents will vary in direct proportion to the changesin the voltagesEr and'Ez. When E1 equals E2 the circuit is balanced and I1 equals 12; This is the usual condition foundin a balance or diflerentialrelay circuit of the type used heretofore.

I" have discovered that this condition may be changed in an advantageous way insofar as relay operation is concerned by connecting into eac-hofthe ammeter circuits a device whose rel sistance-varies greatlywith currentdensity. The most common example of a device of this kind is a current rectifier of the dry contact type or a rectifier of the barrier layer type exemplified by the copper-oxide rectifier.

Accordingly, if the copper-oxide rectifiers l1 and is are connected in the circuits of ammeters l4 and I5, respectively, a decided change occurs in the performance of this circuit as indicated by the curves of Fig. 3.

Fig. 3 shows the relative changes in the ammeter currents resulting from changes in voltages E1 and E2. In this instance current Values are plotted against per cent unbalance of the circuit. When the rectifier devices I! and I8 are eliminated from the ammeter circuits the current variation is illustrated by the solid lines I1 and I2,

I1 being the current flowing through ammeter l4 and Is the current flowing through ammeter Hi. If the rectifier devices I1 and I8 are connected in the ammeter circuits, as shown in Fig. l, the ammeter currents for the same degree of unbalance are illustrated by the dashed lines I1 and I2.

Thus it will be apparent that the ammeter currents are magnified to a considerable extent for the same degree of unbalance of the voltages E1 and E2 due to the functioning of the rectifier devices l1 and I8. This functioning of the rectifiers is more pronounced in the low current ranges where the current density is low and resuits from the inherent characteristics of the rectifier of changing its resistance to a greater extent than a corresponding change in the voltage.

A practical application of the principles of the invention is illustrated in Fig. 2 in the form of a balance or differential relay control system. In

this instance the ammeters I4 and I are replaced by the operating windings l9 and of the differential relay 2|. This relay is of well known construction comprising a pivotally mounted member 22 carrying contact members 23 and 24 and which is actuated in opposite directions by the armatures 25 and 26 in response to the energization of the windings l9 and 20.

In the operation of this system when the voltages E1 and E: are equal, the currents fiowingthrough the circuits of windings I9 and 20, i. e., currents I1 and I2 are also equal. When a variation or change occurs in either one or both of the voltages E1 and E2, resulting in an unbalance of the circuit, the resulting current change is in general as illustrated in Fig. 3 and is the same as explained in connection with Fig. 1.

Accordingly, it will be apparent that when the rectifier devices I! and I8 are used the magnification of the current change in the operating windings l9 and 20 in response to a predetermined change in voltage greatly increases the sensitivity of the differential relay 2| causing it to respond to smaller voltage variations than would otherwise be possible.

The sensitivity of the system may be varied to some extent by either inserting resistance in series with the rectifier devices I! and I8 or chang ing their current density.

'This improved operation of the relay not only increases its effectiveness in control applications where it is already in use, but increases its field of application considerably. The increased sensitivity of the relay without the use of expensive and complicated auxiliary equipment adapts it for use in applications where first cost is an important factor.

In view of the foregoing, it will be apparent that the invention provides a simple and inexpensive difierential relay control system which may be economically and readily applied to perform any desired control operation in response to predetermined variations in voltage.

While the illustrated embodiment of the invention constitutes a practical and useful example thereof, it is to be understood that other embodiments thereof may be made without departing from the spirit of the invention as defined in the appended claims.

I claim as my invention:

1. The combination with a pair of direct-current electric circuits having one common conductor, of a balance relay having opposed operating windings, a resistor, circuit means individually connecting the relay operating windings across said circuits through said resistor to render the relay responsive to voltage differences of the circuits, said resistor being in series circuit relation to both operating windings, and rectifier means of the contact type connected in said circuit means in series circuit relation with each of the relay operating windings, each of said rectifier means being connected to pass current from the positive to the negative conductors of the electric circuits in the low resistance direction of the rectifier means, thereby to render the balance relay more sensitive to the voltage diifcrences of the electric circuits as the result of the inherent characteristics of the rectifier means of decreasing their effective resistance to current fiow in accordance with current density and to a greater extent than a corresponding change in voltage, and the functioning of the resistor to vary the current flow in one operating winding in response to and in the opposite sense to a variation in the current fiow in the other operating winding.

2. The combination with a pair of direct-current circuits comprising a common conductor of one polarity and a pair of separate conductors each of the same polarity but of the opposite polarity to that of the common conductor, of a balance relay having opposed operating windings, circuit means individually connecting one terminal of each of the relay windings to one of the pair of conductors, additional circuit means including a resistor common to both of the windings connecting the opposite terminals of the windings to the common conductor, said common resistor functioning to tie the circuits of the relay windings together so that a variation in the voltage of either one of the direct-current circuits to which they are connected not only produces a change in the current flowing in the relay wind ing connected to that circuit but also produces a change in the current flowing in the other relay winding connected to the other circuit in the opposite sense due to the voltage drop in the common resistor, and rectifier means of the type having a variable resistance dependent upon current density connected in series circuit relation with each of the relay windings to amplify the current change therein to a greater extent than a corresponding change in voltage, whereby the balance relay is rendered more sensitive to the voltage unbalance of the two circuits and its unbalance magnified through the combined functioning of said common resistor and the rectifier means to produce a magnified percentage of unbalance between the currents flowing in the relay windings in response to a variation in the voltage of either direct-current circuit.

MAURICE E. REAGAN. 

